It seems that if there is quite lot of corpses on one square (~125) then game crashes and can break savegame as well... it happened to me when I discovered ZOO in first door next to teleport. So I teleported back and started to kill them from safe distance (yeah I am coward but there were 211 monsters! ) When I killed ~150 of them then game crashed. So I loaded last save, went back for ZOO guys and start killing them again. Then I was doing regural saves after each few dozens of kills in order to find some close-to critical value save but my last attempt has broken save itself (it was very very close to critical crashing value with ~125 bodies on one square). I am adding it zipped
I realized that mine ~125 number is very close to 128 ... so it is probable that game engine can handle "only" 128 corpses/items per square?